Connected: An Internet Encyclopedia
RFC 1700 - introduction

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    INTRODUCTION

    The files in this directory document the currently assigned values for
    several series of numbers used in network protocol implementations.

    	ftp://ftp.isi.edu/in-notes/iana/assignments

    The Internet Assigned Numbers Authority (IANA) is the central
    coordinator for the assignment of unique parameter values for Internet
    protocols.  The IANA is chartered by the Internet Society (ISOC) and
    the Federal Network Council (FNC) to act as the clearinghouse to
    assign and coordinate the use of numerous Internet protocol
    parameters.

    The Internet protocol suite, as defined by the Internet Engineering
    Task Force (IETF) and its steering group (the IESG), contains numerous
    parameters, such as internet addresses, domain names, autonomous
    system numbers (used in some routing protocols), protocol numbers,
    port numbers, management information base object identifiers,
    including private enterprise numbers, and many others.

    The common use of the Internet protocols by the Internet community
    requires that the particular values used in these parameter fields be
    assigned uniquely.  It is the task of the IANA to make those unique
    assignments as requested and to maintain a registry of the currently
    assigned values.

    Requests for parameter assignments (protocols, ports, etc.) should be
    sent to .

    Requests for SNMP network management private enterprise number
    assignments should be sent to .

    The IANA is located at and operated by the Information Sciences
    Institute (ISI) of the University of Southern California (USC).

    If you are developing a protocol or application that will require the
    use of a link, socket, port, protocol, etc., please contact the IANA
    to receive a number assignment.

            Joyce K. Reynolds
            Internet Assigned Numbers Authority
            USC - Information Sciences Institute
            4676 Admiralty Way
            Marina del Rey, California  90292-6695

            Electronic mail: IANA@ISI.EDU
            Phone: +1 310-822-1511

    Most of the protocols are documented in the RFC series of notes.  Some
    of the items listed are undocumented.  Further information on
    protocols can be found in the memo, "Internet Official Protocol
    Standards" (STD 1).

    Data Notations

    The convention in the documentation of Internet Protocols is to
    express numbers in decimal and to picture data in "big-endian" order
    [COHEN].  That is, fields are described left to right, with the most
    significant octet on the left and the least significant octet on the
    right.

    The order of transmission of the header and data described in this
    document is resolved to the octet level.  Whenever a diagram shows a
    group of octets, the order of transmission of those octets is the
    normal order in which they are read in English.  For example, in the
    following diagram the octets are transmitted in the order they are
    numbered.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       1       |       2       |       3       |       4       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       5       |       6       |       7       |       8       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       9       |      10       |      11       |      12       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Transmission Order of Bytes

    Whenever an octet represents a numeric quantity the left most bit in the
    diagram is the high order or most significant bit.  That is, the bit
    labeled 0 is the most significant bit.  For example, the following
    diagram represents the value 170 (decimal).

                              0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |1 0 1 0 1 0 1 0|
                             +-+-+-+-+-+-+-+-+

                            Significance of Bits

    Similarly, whenever a multi-octet field represents a numeric quantity
    the left most bit of the whole field is the most significant bit.  When
    a multi-octet quantity is transmitted the most significant octet is
    transmitted first.

    Special Addresses

    There are five classes of IP addresses: Class A through Class E.  Of
    these, Classes A, B, and C are used for unicast addresses, Class D is
    used for multicast addresses, and Class E addresses are reserved for
    future use.

    With the advent of classless addressing [CIDR1, CIDR2], the
    network-number part of an address may be of any length, and the whole
    notion of address classes becomes less important.

    There are certain special cases for IP addresses.  These special cases
    can be concisely summarized using the earlier notation for an IP
    address:

          IP-address ::=  { ,  }

             or

          IP-address ::=  { , ,
                                                           }

    if we also use the notation "-1" to mean the field contains all 1
    bits.  Some common special cases are as follows:

          (a)   {0, 0}

             This host on this network.  Can only be used as a source
             address (see note later).

          (b)   {0, }

             Specified host on this network.  Can only be used as a
             source address.

          (c)   { -1, -1}

             Limited broadcast.  Can only be used as a destination
             address, and a datagram with this address must never be
             forwarded outside the (sub-)net of the source.

          (d)   {, -1}

             Directed broadcast to specified network.  Can only be used
             as a destination address.

          (e)   {, , -1}

             Directed broadcast to specified subnet.  Can only be used as
             a destination address.

          (f)   {, -1, -1}

             Directed broadcast to all subnets of specified subnetted
             network.  Can only be used as a destination address.

          (g)   {127, }

             Internal host loopback address.  Should never appear outside
             a host.

    REFERENCES

    [COHEN]   Cohen, D., "On Holy Wars and a Plea for Peace", IEEE Computer
              Magazine, October 1981.

    [CIDR1]   Fuller, V., T. Li, J. Yu, and K. Varadhan, "Classless
              Inter-Domain Routing (CIDR): an Address Assignment and
              Aggregation Strategy", RFC 1519, September 1993.

    [CIDR2]   Rekhter, Y., and T. Li, "An Architecture for IP Address
              Allocation with CIDR", RFC 1518, September 1993.

    []

Connected: An Internet Encyclopedia
RFC 1700 - introduction